Artificial turf has been developed to cover exposed surfaces with a material resembling lawns or grassy areas and which are exposed to the elements and must be able to retain their appearance and wear properties even after much usage and severe treatment, while permitting moisture, e.g. rain, to pass through to the underlying substrate. The latter substrate can be ground which is capable of absorbing the water or concrete or some other base which can be formed with drains which permit the water passing through the artificial turf of accumulate and be drawn off.
The synthetic grass may comprise an upper layer of cut pile, composed of a weather-resistant synthetic resin monofilament and anchored to a support layer which is provided with voids which can be traversed by the water.
The pile can be anchored to the support by thermal welding, by needling through the support and/or by the application of adhesives or bonding agents which should also be resistant to weathering and do not tend to decompose, mold or decay in a moist state.
Synthetic turfs have also been formed from molded thermoplastic materials which are perforated to provide openings through which the water can pass, and formed with projections adapted to simulate natural ground cover.
In practically all of the above-described cases, the artificial turf must be provided with means for permitting drainage away from the reverse side of the ground covering, especially when an exterior use is planned.
However, the various methods of providing such drainage means heretofore have created an assortment of problems.
For example, it is known to provide a drainage-promoting arrangement in the form of projections from the reverse side of the artificial turf, e.g. as plugs, having a hemispherical configuration and composed of synthetic resin material, rubber or the like.
Such coverings are primarily used to cover concrete surfaces, balconies, aprons surrounding swimming pools and the like.
An important disadvantage of such devices is that repeated walking over the surface of the ground covering induces a migration of the ground covering upon the supporting surface. Apparently, as the user takes a step upon the ground covering, the foot pressure causes pivoting about the projections on the reverse side of the ground covering and a component of movement of the latter in the opposite direction to the orientation of the fibers on the surface. Some of the components may be contributed by pivotal action directly at the pile surface.
Regardless of the cause, the artificial turf undergoes a barely perceptible movement with each step. After eight hours of heavy traffic upon the covering, however, a displacement of several scores of centimeters can be detected.